Re: Unknown SQL

>And in fact, from a pragmatical point of view, the fact that RDBMSs are
>largely standardized, it is much easier to switch to different languages or
>even RDBMS vendors. Same can not be said for OODBMSs. Some argue that this
>is not a strength of the relational model, but rather a failure (since
 what?
>10 years?) on the part of the OODBMS vendors to get their act together on
 the
>standardization front. Others will argue that it _is_ easier to standardize
>implementations of well understood technology such as relational theory,
 and
>that object oriented persistence is difficult simply because there is no
>overarching formal theory for objects.

Philip,

It is not an issue of theory, per se, that makes it easy to switch between RDBMSs and hard to switch between network model OODBMSs. An RDBMS "represents all data as values in columns in relations". The value 1 does not change significantly among different representations. Whether represented with a character string, packed decimal, binary integer, IEEE floating point number or any other representation, the value 1 remains the value 1.

Moving from one vendor's RDBMS to another vendor's RDBMS, the value 1 likewise remains the value 1. Similarly, the value 346987563 remains the value 346987563.

Network model databases, however, represent data with pointers and other physical constructs that vary greatly among different vendors. Further issues such as shallow copies vs. deep copies, pointer swizzling, implicit back-pointers etc. vary as well. Every different implementation of network model database changes the meaning of the data implied by physical constructs by introducing often subtle differences in interpretation.

Regards,
Bob Received on Sat May 12 2001 - 13:07:24 CEST